THS4521 datasheet(25/48 Pages) TI

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THS452x

OUT-

OUT+

Single-Ended

Input

Differential

Output

S+

S-

THS452x

OUT-

IN-

OUT+

IN+

Differential

Input

Differential

Output

S+

S-

OUT+ ´

R +R

IN- ´

R +R

THS4521

THS4522

THS4524

www.ti.com

SBOS458D – DECEMBER 2008 – REVISED AUGUST 2010

APPLICATION INFORMATION

The following circuits show application information for

the THS4521, THS4522, and THS4524 family. For

simplicity, power-supply decoupling capacitors are

not shown in these diagrams; see the EVM and

Layout Recommendations section for suggested

guidelines. For more details on the use and operation

of fully differential op amps, refer to the Application

Report

Fully-Differential

Amplifiers

(SLOA054),

available for download from the TI web site at

www.ti.com.

Differential Input to Differential Output

Amplifier

The THS4521, THS4522, and THS4524 family are

fully-differential operational amplifiers that can be

Figure 61. Single-Ended Input to Differential

used to amplify differential input signals to differential

Output Amplifier

output signals. Figure 60 shows a basic block

diagram of the circuit (VOCM and PD inputs not

shown). The gain of the circuit is set by RF divided by

Input Common-Mode Voltage Range

RG.

The input common-mode voltage of a fully-differential

op amp is the voltage at the + and – input pins of the

device.

It is important to not violate the input common-mode

voltage range (VICR) of the op amp. Assuming the op

amp is in linear operation, the voltage across the

input pins is only a few millivolts at most. Therefore,

finding the voltage at one input pin determines the

input common-mode voltage of the op amp.

Treating the negative input as a summing node, the

voltage is given by Equation 1:

(1)

Figure 60. Differential Input to Differential Output

To determine the VICR of the op amp, the voltage at

Amplifier

the negative input is evaluated at the extremes of

VOUT+. As the gain of the op amp increases, the input

Single-Ended Input to Differential Output

common-mode voltage becomes closer and closer to

Amplifier

the input common-mode voltage of the source.

The THS4521, THS4522, and THS4524 family can

also amplify and convert single-ended input signals to

Setting the Output Common-Mode Voltage

differential output signals. Figure 61 illustrates a basic

The output common-model voltage is set by the

block diagram of the circuit (VOCM and PD inputs not

voltage at the VOCM pin. The internal common-mode

shown). The gain of the circuit is again set by RF

control circuit maintains the output common-mode

divided by RG.

voltage within 5-mV offset (typ) from the set voltage.

If left unconnected, the common-mode set point is set

to midsupply by internal circuitry, which may be

overdriven from an external source.

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Product Folder Link(s): THS4521 THS4522 THS4524

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